Power supply for use with electrodynamic screen

ABSTRACT

An AC power supply for connection to at least one electrode of an electrodynamic screen includes a DC-to-DC converter electrically coupled to a source of DC voltage including an output. The system includes a DC-to-AC converter electrically coupled to the output of the DC-to-DC converter, including a two-terminal passive element electrically coupled in series with a first transistor including a control terminal electrically coupled to a periodic voltage signal configured to switch the first transistor between an on/off state. The system includes an AC output including an AC voltage configured to change periodically. The system includes a regulator circuit configured to sample the AC output voltage and detect when the AC output voltage reaches a predetermined voltage. The regulator circuit is configured to electrically couple the power supply to the source of DC voltage when the output voltage is less than the predetermined voltage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication Ser. No. 63/210,336 filed on Jun. 14, 2021, the entirety ofwhich is incorporated by reference herein.

BACKGROUND OF THE DISCLOSED SUBJECT MATTER Field of the DisclosedSubject Matter

The disclosed subject matter relates to a system for removing particlesfrom transparent surfaces. In particular, the present disclosed subjectmatter is directed toward a power supply to be used with anelectrodynamic screen (EDS) for the purpose of removing dust and othersmall particles from surfaces upon which such particles haveaccumulated. Examples include the use of EDS technology to cleanphotovoltaic (PV) panels, solar-water heaters, and concentratingreflectors used in solar power systems and heating applications, alsoknown as concentrated solar power (CSP) reflectors. Other uses of theEDS may include the cleaning of mirrors, lenses, telescope apertures,and other optical systems, displays, electronic screens, portals,windows, and floors, as well as applications requiring the transport ofparticles. Basically, EDS technology can be used to clean particles ofdust or other contaminants from most non-conducting surfaces.

In the area of solar power, photovoltaic and concentrated solar powerhave the potential to contribute substantially to worldwide energy needsas a means for reducing the burning of fossil fuels for energy. Largeinstallations of PV or CSP at the megawatt (MW) or higher-level capacityare often located in arid desert regions of the globe where sunlight isplentiful, land is cheap, solar flux is high, and clouds and rain arescarce. While such desert regions are the sunniest on Earth, they arealso among the dustiest locations in the world. Dust particles,generally in the form of fine sand, often deposit on such solarcollectors, thereby obscuring sunlight and reducing total power outputof the solar plant. This phenomenon is also called “soiling” in thefield of solar power. As an example of the problem, a deposit of just 4grams-per-square meter of dust particles in the size range 0.5 to 10microns can reduce the power output of a solar plant by as much as 40%of that obtainable with dust-free collectors.

In another example, and in no way limiting the application thereof,optical systems such as lenses, typically, but not limited to those usedin outdoor environments, may also suffer from the accumulation of dustand other particles. Keeping such systems in optimal working orderrequires that critical lens surfaces be kept dust free. Similarly, thesurfaces of building windows may suffer from particle accumulation,particularly in desert environments.

DESCRIPTION OF RELATED ART

A variety of methods and systems are known for removing dust fromsurfaces. Systems for maintaining clean solar panels and solarconcentrators have been developed in the past. Some have involved manualcleaning using soft brushes with water and detergents. Such manualmethods of cleaning are generally labor intensive, adding significantlyto the cost of cleaning. Some technologies developed for cleaning PVpanels have relied on robotic devices that travel on rails or slides toremove dust via rotating brushes. Other cleaning techniques have usedwipers or vibrators as a way to remove accumulated dust. Yet otherautomated systems apply flowing water or spray directly onto solarcollectors. Each of these methods suffers from drawbacks known in theart, including vulnerable moving parts and adverse water consumption.These contact cleaning methods also abrade the surface, which in thecase of solar panels for example, can wear away anti-reflectivecoatings, resulting in a permanent 2-3% loss of power output.

Another technique for removing dust relies on electrostatic forces tomove the particles. In such systems, an electrodynamic screen (EDS) isformed by depositing a set of two or more interdigitated, conductiveelectrodes on a glass, polymer, or other insulating substrate. Theseelectrodes are energized by poly-phased voltages, with the systemtypically comprising, but not limited to, three electrode sets and threevoltage phases. Electrode voltages, which can be applied at any suitableamplitude, typically have magnitudes between 500 V and 3,000 V atfrequencies over the range 1 to 100 Hz. Other voltages and frequenciesare also possible. The interdigitated electrodes produce a laterallymoving, traveling wave of electrostatic field. This field exerts coulomband other forces on deposited particles, thereby lifting them off thesurface and transporting them to an outer edge of the screen. In solarapplications, this clearing of particles substantially restores thepower output of the collector.

One critical component of an EDS system is the power supply thatenergizes the electrodes. The EDS power supply must provide a periodic,alternating voltage to each electrode, in the proper phase, so as toproduce a moving wave of electrostatic field at the EDS surface. Thelatter is necessary to move dust particles off the surface of the EDSscreen. Many developers of EDS devices have relied on expensivelaboratory-grade or “benchtop” power supplies to produce the neededvoltages. Others have developed custom-designed power supplies that aremade at considerable cost due to the use of many expensive or specialtyparts. It is generally accepted, however, that the expected widespreadgrowth of solar power will require plants to produce power at as low acost as possible, thereby requiring inexpensive power supplies. For thepurposes of this disclosure, “periodic” is characteristic of an entity,such as a signal, to repeat one or more values, sequences or steps atregular intervals or periods.

Previous power supplies used for EDS systems in the laboratory consumemany watts of power and have large physical form factors. This drawbackis particularly true for DC power supplies in the kilovolt range.Commercial kilovolt-level DC-to-DC converters exist, and some of thesepower supplies are compact and consume little power, but their pricesdiscourage their use in large-scale solar power installations where lowcost is a significant factor. What is needed is an inexpensive powersupply that can reliably perform under myriad of conditions. Such apower supply must be capable of producing poly-phase voltages,preferably in the kilovolt range, at frequencies in the typical range ofabout 1 Hz to 100 Hz.

One embodiment of the power supply disclosed herein makes use of thecascaded-boost converter (CBC) configuration of switching power supply.This type of DC-to-DC (DC/DC) converter, shown in its basic form inprior-art FIG. 3 , is described in both the technical literature and inseveral prior-art patents. For example, the cascaded-boost converter isexplained in depth in “A 300-Watt Cascaded Boost Converter Design forSolar Energy Systems” by A. Al Nabulsi et all (IEEE InternationalConference on Electric Power and Energy Conversion Systems, 2009), andin Fundamentals of Power Electronics by Robert Erickson and DraganMaksimovic (Springer 2020). Embodiments of the disclosed invention maybe based on other types of switching power supplies, including classicboost converters, buck/boost converters, and linear power supplies thatare not of the switching type.

The disclosed power-supply modifications, specifically designed for usewith an electrodynamic screen, add additional features to such classicconfigurations, such as the cascaded-boost embodiment, to produce alow-cost power supply suitable for use with EDS technology.

SUMMARY OF THE DISCLOSED SUBJECT MATTER

The purpose and advantages of the disclosed subject matter will be setforth in and will be apparent from the description that follows and willbe learned by practice of the disclosed subject matter. Additionaladvantages of the disclosed subject matter will be realized and attainedby the methods and systems particularly pointed out in the writtendescription and claims hereof, as well as from the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the disclosed subject matter, as embodied and broadly describedherein, the disclosed subject matter includes a method of high voltagegeneration by using a switching power supply, wherein the converteroperates with a minimally power-consuming, load. Such a scenario mayarise when the converter drives a capacitive load, such as theelectrodes of an EDS device. Some existing high-voltage power suppliesthat are suitable for driving capacitive loads convert a low-voltage,“direct-current” (DC) input to a low-voltage “alternating current” (AC)output. The latter (AC current) is then fed to a transformer which stepsup the voltage. The transformer output may then be rectified, if needed,to produce high-voltage DC. The disclosed power-supply configurationproduces high-voltage DC without using a transformer and withoutintermediate DC-to-AC conversion. It also allows for the conversion ofhigh-voltage DC into a high-voltage AC output.

The disclosed subject matter includes a system for producing bothsingle-phase and poly-phase high-voltage AC. It also includes a methodfor regulating the peaks of the single or poly-phase voltage output(s)using an analog, hysteretic, two-position controller. The disclosedcontroller can modulate the frequency of the AC output while alsoregulating its peak voltage. Inasmuch as some EDS devices are prone toelectrical breakdown between electrodes if the applied voltage is toohigh, such regulation has the advantage that it protects its EDS loadfrom breakdown while also protecting power-supply components from unduestress due to overvoltage. The controller is designed so that it can beimplemented using low-cost, commercial, “off the shelf” componentsgenerally available from commercial parts vendors.

To achieve these and other advantages and in accordance with the purposeof the disclosed subject matter, as embodied and broadly describedherein, the disclosed subject matter includes a system for an AC powersupply for connection to at least one electrode of an electrodynamicscreen, the power supply including a DC-to-DC converter electricallycoupled to a source of DC voltage, the DC-to-DC converter furtherincluding an output of the DC-to-DC converter. The system includes aDC-to-AC converter electrically coupled to the output of the DC-to-DCconverter, the DC-to-AC converter further including a two-terminalpassive element electrically coupled in series with a first transistor,the first transistor including a control terminal, wherein the controlterminal of the first transistor is electrically coupled to a periodicvoltage signal configured to switch the first transistor into an onstate and an off state. The system includes an AC output, the AC outputincluding an AC voltage configured to change periodically. The systemincludes a regulator circuit configured to sample the AC output voltageof the power supply, the regulator circuit further configured to detectwhen the AC output voltage reaches a predetermined voltage, and whereinthe regulator circuit is configured to electrically couple the powersupply to the source of DC voltage when the output voltage is less thanthe predetermined voltage.

In embodiments of the present subject matter, the periodic voltagesignal is configured to control the on/off state of the at least atransistor causes the AC output to transition periodically, at apredetermined frequency, between zero and a positive or negative voltageof a magnitude larger than zero.

In embodiments of the present subject matter, the periodic voltagesignal comprises a frequency, the frequency configured to vary.

In embodiments of the present subject matter, the regulator circuitincludes a second transistor configured to connect and disconnect thepower supply to the source of DC voltage.

In embodiments of the present subject matter, the DC-to-DC converter isa cascaded-boost converter.

In embodiments of the present subject matter, the second transistor is ap-channel MOSFET.

In embodiments of the present subject matter, the cascaded-boostconverter operates in a discontinuous mode.

In embodiments of the present subject matter, the output voltage isapplied to at least one electrode of an electrodynamic screen, theelectrode including a capacitance electrically coupled in parallel withthe AC output of the power supply.

In embodiments of the present subject matter, the periodic voltagesignal configured to control the on/off state of the first transistorcauses the AC output of the power supply to transition periodicallybetween a positive voltage and a negative voltage.

In embodiments of the present subject matter, the periodic voltagesignal includes a frequency, the frequency configured to change overtime.

In embodiments of the present subject matter, the periodic voltage isproduced by an astable multivibrator.

In embodiments of the present subject matter, the AC output includes aplurality of distinct AC outputs.

In embodiments of the present subject matter, the plurality of distinctAC outputs apply poly-phased voltages to a plurality of electrodes of anelectrodynamic screen.

In embodiments of the present subject matter, the number of poly-phasedvoltages is between two and five.

In embodiments of the present subject matter, the AC output voltage ofthe power supply is configured to transition periodically between avoltage near zero and a voltage, wherein the voltage comprises amagnitude no larger than one kilovolt.

In embodiments of the present subject matter, the magnitude of the ACoutput voltage of the power supply is configured to increase inmagnitude to a predetermined value that is larger than one kilovolt.

To achieve these and other advantages and in accordance with the purposeof the disclosed subject matter, as embodied and broadly describedherein, the disclosed subject matter includes a system for an analoghysteretic two-position regulator circuit for use with a power supply,the regulator circuit including a Schmitt trigger, the Schmitt triggerfurther including an input to the Schmitt trigger, the input beingderived from an output of a voltage sampling circuit electricallycoupled to a power supply output. The system includes an output from theSchmitt trigger. The system includes a first comparator comprising aninput to the first comparator, the input to the first comparatorelectrically coupled to the output from the Schmitt trigger via a firstresistor and a second comparator comprising an output from the secondcomparator, the output from the second comparator electrically coupledto the input to the Schmitt trigger via a second resistor. The secondcomparator further includes an input to the second comparator, the inputto the second comparator electrically coupled to a periodic voltagesignal. The system includes a resistor network electrically coupled to apower supply input voltage and a reference ground, the resistor networkconfigured to provide a reference voltage. The system includes thereference voltage electrically coupled to a second input of the firstcomparator and a second input of the second comparator. The systemincludes a cascaded boost converter, the cascaded boost convertercomprising an input voltage terminal. The system includes a transistorconfigured to switch between an on state and an off state, thetransistor electrically coupled between the power supply input voltageand the input voltage terminal of the cascaded boost converter, thetransistor comprising a control terminal, the control terminalelectrically coupled to the output of the first comparator. Thetransistor configured to switch to the on state in response to an outputvoltage of the cascaded boost convert, wherein the output voltage of thecascaded boost converter is below a predetermined threshold. Thetransistor further configured to switch to the off state in response toan output voltage of the cascaded boost converter wherein the outputvoltage of the cascaded boost converter is above the predeterminedthreshold.

In embodiments of the present subject matter, the regulator circuitfurther includes a tunable, pulsed-output voltage regulation and timingsystem, the tunable, pulsed-output voltage regulation and timing systemfurther including a cascaded-boost converter.

In embodiments of the present subject matter, the regulator circuitincludes a plurality of distinct regulator circuits configured to beelectrically coupled.

In embodiments of the present subject matter, the regulator circuitincludes between two and five distinct regulator circuits.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and are intended toprovide further explanation of the disclosed subject matter claimed.

The accompanying drawings, which are incorporated herein and constitutepart of this specification, are included to illustrate and provide afurther understanding of the method and system of the disclosed subjectmatter. Together with the description, the drawings serve to explain theprinciples of the disclosed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of various aspects, features, and embodiments ofthe subject matter described herein is provided with reference to theaccompanying drawings, which are briefly described below. The drawingsare illustrative and do not reflect the physical size of the disclosedcircuitry. The drawings in schematic form illustrate various aspects andfeatures of the present subject matter and may illustrate one or moreembodiment(s) or example(s) of the present subject matter in whole or inpart.

FIG. 1 is a diagram of a prior-art power supply.

FIG. 2 is a diagram of the overall configuration of the power supplyincorporating aspects of the disclosed invention.

FIG. 3 is a schematic representation of a prior-art cascaded-boostconverter driving a load.

FIG. 4 shows one implementation of the disclosed invention using acascaded-boost converter.

FIGS. 5A and 5B show waveforms relevant to the circuit of FIG. 4 .

FIG. 6 is a representation of one aspect of the disclosed inventionwherein the power-supply module has a series output impedance.

FIG. 7 shows a version of the circuit incorporating an analog hystereticfeedback circuit.

FIG. 8 shows the details of one embodiment of the analog hystereticfeedback circuit of FIG. 7 .

FIG. 9 illustrates exemplary waveforms for the circuit of FIG. 7 .

FIG. 10 shows exemplary waveforms for a three-phase version of thedisclosed power supply.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Reference will now be made in detail to exemplary embodiments of thedisclosed subject matter, examples of which are illustrated in theaccompanying drawings. The method and corresponding steps of thedisclosed subject matter will be described in conjunction with thedetailed description of the system.

The methods and systems presented herein may be used for producingpoly-phase voltages at the kilovolt level over an approximate frequencyrange of 1 to 100 Hz. It is understood that voltages more than, or lessthan, one kilovolt are to be included within the scope of the invention.Likewise, AC voltage output frequencies within this general range, buthigher or lower in frequency, are to be included within the scope of theinvention. The disclosed power supply configuration is particularlysuited for use in driving an electrodynamic screen for the purpose ofremoving dust particles from the surfaces of solar collectors. Thedeposition of such particles in a solar power plant can significantlyreduce power output capability. For the purposes of this disclosure, a“power supply” is a device configured to supply electric power to anelectrical load. Additionally or alternatively, a power supply may beconfigured to convert electric current from a source to the correctvoltage, current and frequency to the electrical load. For example andwithout limitation, the power supply may be a standalone component orbuilt into a larger system or plurality of connected components.

In FIG. 1 , a prior-art power-supply module 100 is adapted to beconnected to a source 101 of DC power that applies V_(DC) to the V_(IN)input 102 of the power-supply module. Power-supply module 100 producesan output voltage 103 (V_(OUT)) that is applied across the terminals ofload 104. Load 104 can be a resistor, capacitor, other circuit element,or any other circuit or electrical system requiring voltage. For thepurposes of this disclosure, “electrically coupled” is the configurationreferring to one or more components being connected by at least aconductor or means for transferring electrical energy.

For the purpose of explanation and illustration, and not limitation, anexemplary embodiment of the system in accordance with the disclosedsubject matter is shown in FIG. 2 . FIG. 2 shows additional elementsadded to power-supply module 100. These additional elements compriseportions of the disclosed invention. Regulator 105 is a circuitconnected in series between one terminal of the input voltage source 101and a corresponding terminal of the V_(IN) input 102. Regulator 105receives a voltage representative of V_(OUT) 103 via feedback path 107to communicate to regulator 105 the instantaneous value of output 103for the purpose of regulating V_(OUT). A DC-to-AC converter circuit 106,connected at output terminals 108 of the DC-to-DC converter 100, acts toconvert the voltage output of converter 100 into V_(AC), whichconstitutes an AC output 109 suitable for driving load 104. For thepurposes of this disclosure, “terminal” is the point at which aconductor from a component, device or network comes to an end. Terminalmay also refer to an electrical connector at this endpoint, acting asthe reusable interface to a conductor and creating a point whereexternal circuits can be connected. A terminal may simply be the end ofa wire or it may be fitted with a connector or fastener.

FIG. 3 shows prior-art circuit 200 based on the topology of thecascaded-boost converter (CBC) known in the art. Circuit 200 comprisesone prior-art embodiment of the DC-to-DC converter circuit 100 shown inFIG. 1 . In FIG. 3 , a first terminal of inductor L₁ is connected to theanodes of diodes D₁ and D₂. A second terminal of L₁ is adapted to beconnected to one terminal of DC source. The cathode of D₁ is connectedto a first terminal of inductor L₂, and the cathode of diode D₂ isconnected to a second terminal of inductor L₂. Capacitor C₁ is connectedbetween the cathode of diode D₁ and reference ground 205. Transistor M₁,in this embodiment an n-channel, metal-oxide-semiconductor field-effecttransistor (MOSFET), is connected between the cathode of diode D₂ andreference ground 205. Transistor M₁ operates as a switch.

For the purposes of this disclosure, a “transistor” is a semiconductordevice configured to switch and/or amplify electrical signals and power.When configured as a switch, a transistor may include an “off” and “on”states or phases. Important parameters for this application include thecurrent switched, the voltage handled, and the switching speed,characterized by the rise and fall times. Parameters are chosen suchthat the “off” output is limited to leakage currents may be too small toaffect connected circuitry, the resistance of the transistor in the “on”state may be too small to affect circuitry, and the transition betweenthe two states may be fast enough not to have a detrimental effect.

According to embodiments of the disclosed subject matter, transistorssuch as bipolar transistors may be used in switching applications, andrequires biasing the transistor so that it operates between its cut-offregion in the off-state and the saturation region (on). This requiressufficient base drive current. As the transistor provides current gain,it facilitates the switching of a relatively large current in thecollector by a much smaller current into the base terminal. The ratio ofthese currents varies depending on the type of transistor, and even fora particular type, varies depending on the collector current.

For the purposes of this disclosure, a “switch” is an electricalcomponent configured to disconnect or connect the conducting path in anelectrical circuit, interrupting the electric current or diverting itfrom one conductor to another. According to embodiments of the presentdisclosure, a switch may include one or more switches or types ofswitches. For example and without limitation, a switch may include setsof contacts controlled by the same knob or actuator, and the contactsmay operate simultaneously, sequentially, or alternately. A switch maybe operated manually, for example, a light switch or a keyboard button,or may function as a sensing element. Many specialized forms exist, suchas the push-button switch, reversing switch, relay, and circuit breaker.According to embodiments of the present subject matter, one or switchesconfigured for use in high-powered circuits may have specialconstruction to prevent destructive arcing when they are opened.

The anode of diode D₃ is connected to the cathode of diode D₂ and thesecond terminal of inductor L₂. The cathode of diode D₃ is connected tothe positive (+) terminal of output voltage V_(OUT) which is applied toload 104. Storage capacitor C₂ is connected between the (+) side of TOUTand reference ground 205.

The control terminal of transistor M₁, generally the gate terminal of aMOSFET, is driven by pulse-width-modulated (PWM) control signal 208. ThePWM signal may be derived from one of any astable multi-vibratorcircuits known in the art, for example from a 555-timer integratedcircuit or microcontroller. For the purposes of this disclosure, the“pulse-width-modulated (PWM) control signal is a modulation techniquethat generates variable-width pulses to represent the amplitude of aninput signal. For the purposes of this disclosure, an “astablemultivibrator” includes two amplifying stages connected in a positivefeedback loop by two capacitive-resistive coupling networks in which thecircuit is not stable in either state, it continually switches from onestate to the other. The circuit has two astable (unstable) states thatchange alternatively with maximum transition rate because of the“accelerating” positive feedback. It is implemented by the couplingcapacitors that instantly transfer voltage changes because the voltageacross a capacitor cannot suddenly change. In each state, one transistoris switched on and the other is switched off. Accordingly, one fullycharged capacitor discharges (reverse charges) slowly thus convertingthe time into an exponentially changing voltage. At the same time, theother empty capacitor quickly charges thus restoring its charge (thefirst capacitor acts as a time-setting capacitor and the second preparesto play this role in the next state). The circuit operation is based onthe fact that the forward-biased base-emitter junction of theswitched-on bipolar transistor can provide a path for the capacitorrestoration.

The load 104 is connected between the (+) and (−) terminals of theoutput V_(OUT). This load could be, among other things, a resistor,capacitor, inductor, any combination of these three elements, or anelectronic circuit that requires power from power-supply module 200.

The operation of the cascaded-boost converter of FIG. 3 is known in theart. The circuit is generally analyzed as follows: For the time t_(on)that switching transistor M₁ is on, the change in current throughinductors L₁ and L₂ can be expressed by:

$\begin{matrix}{{{\Delta I_{L1}} = {\frac{V_{IN}}{L_{1}}DT}},{{\Delta I_{L2}} = {\frac{v_{C1}}{L_{2}}DT}},} & (1)\end{matrix}$where T is the period of the PWM signal and D=t_(on)/T is the dutycycle, i.e., the percentage of time of the cycle that M₁ is “on”.Similarly, for the time t_(off) that transistor M₁ is off, the change incurrent through inductors L₁ and L₂ can be expressed by:

$\begin{matrix}{{{\Delta I_{L1}} = {\frac{V_{IN} - v_{C1}}{L_{1}}\left( {1 - D} \right)T}},{{\Delta I_{L2}} = {\frac{v_{C1} - V_{OUT}}{L_{2}}\left( {1 - D} \right)T}}} & (2)\end{matrix}$These equations assume that the forward voltage drops across D₁ and D₂are small relative to V_(IN) and can be neglected in the calculations.Applying the principle of current balance to inductors L₁ and L₂ revealsthat:

$V_{OUT} = \frac{V_{IN}}{\left( {1 - D} \right)^{2}}$which is the expected transfer function for two boost converterscascaded with each other. Of note is the fact that V_(OUT) is larger inmagnitude than V_(IN), because D<1. The preceding analysis is valid onlywhen the CBC delivers sufficient current to the load. If the load 104 isrepresented, for the sake of analysis, as a resistor R_(LOAD), thencurrent V_(OUT)/R_(LOAD) will flow into the load 104. The currentflowing into R_(LOAD) represents the current drawn by a power-consumingload connected across the V_(OUT) terminals. If sufficient load currentis not drawn by the load, then CBC 200 will perform essentially as acurrent source that continually increases the charge stored in outputcapacitor C₂, thereby continually increasing output voltage 103.

It is known in the art that an EDS electrode can be modeled as acapacitive load. If CBC 200 drives an EDS, then output capacitor 111(C₂) will be connected in parallel with such a capacitive load. As notedabove, the parallel combination of these capacitors will be continuallycharged, because the circuitry inside CBC 200 will act essentially as acurrent source charging the capacitances. If neither capacitor C₂ northe EDS-electrode capacitive load succumbs to breakdown due toovervoltage, output voltage 103 of the converter of FIG. 3 will belimited only by the reverse breakdown voltage of diode D₃. Power lossesin the circuit may also limit the charging of capacitor C₂ and the EDScapacitance. For example and without limitation, the EDS may include awindow, a solar/photovoltaic panel, a mirror, an electronic screen,lenses, telescopes, optical systems, portals, windows, electronicdisplays, and floors, or any application requiring the transport ofparticles.

According to Equations (1) and (2), when the load is capacitive, theload cannot draw sufficient current to maintain continuous-modeoperation of the DC/AC converter 106. Thus the converter will operate inthe discontinuous mode, wherein the current that flows into the parallelcombination of C₂ and the EDS load capacitance will depend on the inputvoltage V_(IN), the switching period T, and the duty cycle D of PWMsignal 208. The converter currents will be inversely proportional to theinductance values of L₁ and L₂, as shown in Equations (1) and (2). Thephenomenon of generating high voltages by continually charging acapacitive load is desirable for EDS applications, because voltages inthe kilovolt range can be produced in this way. The problem remains thatwith no or very limited energy dissipative component to load 104, thevoltage across C₂ will rise to an undesirable magnitude unless othermeasures are taken.

The circuit of FIG. 4 shows one embodiment of the DC/AC converter 106connected across terminals 108. Resistor 206, labeled R₂, is connectedin series with M₂ transistor 207 which operates as a switch. The seriescombination of R₂ and M₂ is connected across terminals 108. In theembodiment of FIG. 4 , M₂ is a MOSFET, and the load is capacitor 110(C_(LOAD)). A periodic signal 203 (DCHRG), which generally has a muchlower frequency than PWM signal 208 driving M₁, is connected to thecontrol terminal of M₂, which is the gate of MOSFET 207 in theembodiment of FIG. 4 . While FIG. 4 shows the source of MOSFET 207connected to ground 205, and resistor 206 connected to the positive (+)V_(OUT) terminal, an arrangement wherein the positions are reversed,with the drain of MOSFET 207 connected to the (+) V_(OUT) terminal andthe resistor 206 connected to ground 205, is also within the scope ofthe invention. Likewise, FIG. 4 shows M₁ and M₂ as n-channel MOSFETs,but appropriately connected p-channel MOSFETs or BJT devices could alsobe used.

When periodic signal DCHRG is high in FIG. 4 , transistor M₂ turns on(becomes conducting), effectively connecting R₂ in parallel withC_(LOAD). This connection discharges any voltage across C_(LOAD) with atime constant on the order of R₂(C₂+C_(LOAD)), where C₂ is capacitor111. (It is known in the art the net capacitance of two capacitorsconnected in parallel is equal to their sum). When DCHRG is low, M₂turns off, effectively disconnecting R₂ from the circuit. During thistime interval, the capacitor C₂ inside CBC 200 and C_(LOAD) will becharged together by the circuitry of the CBC.

FIG. 5A generally shows the relationship over time between DCHRG andV_(OUT) for the case were the voltage charging C_(LOAD) has an outputresistance. In some cases, the output of CBC 200 can be modeled as acurrent source of value I₀. In such cases, C₂ in parallel with C_(LOAD)will be charged linearly with slope dv/dt=I₀(C₂+|C_(LOAD)) during theoff phase of M₂. The resulting output voltage for this latter case isshown in FIG. 5B.

An important metric in the design of a CBC which drives a capacitiveload is the time required for the output to rise from zero to somedesired output voltage, for example, to 1.3 kV in one embodiment ofrelevance to the EDS. Because the average current that charges thecombined (C₂+C_(LOAD)) is proportional to the duty cycle D and PWMperiod T (see Equation 1), the CBC can be modeled as having anequivalent “resistance” R_(S) charging (C₂+C_(LOAD)) as follows:

$\begin{matrix}{R_{S} \propto {L\frac{1}{DT}}} & (4)\end{matrix}$The time constant for charging C₂ in the circuit of FIG. 4 can beexpressed as:

$\begin{matrix}{\tau = {{R_{S}\left( {C_{2} + C_{LOAD}} \right)} \propto {L\frac{1}{DT}\left( {C_{2} + C_{LOAD}} \right)}}} & (5)\end{matrix}$The values T=0.167 ms (f=6 kHz) and D=0.6 comprise exemplary parameterssuitable for use in an EDS system, but other values are possible withinthe scope of the invention. These parameters can provide a good balancebetween the charging rate when DCHRG is low, and the power consumptionthat occurs when transistor M₁ switches between its on and off states.These values are also favorable for reducing the effects of second-orderparameters in the circuit, such as the internal series resistances ofinductors L₁ and L₂, forward voltage drops of diodes D₁, D₂, and D₃, andcapacitor dissipation effects. Of note is the fact that the CBC willoperate in the discontinuous conduction mode when the load current istoo small to maintain continuous-mode operation. This phenomenon isconsistent with traditional analysis outlined, for example, inFundamentals of Power Electronics by Erickson and Maksimovic (Springer2020).

FIG. 6 shows the above version of the DC/AC converter 106 connected to amore general version of DC-to-DC converter 100. Internal impedance 210represents the series impedance Z_(S) seen looking into the outputterminals of DC-to-DC converter 100. In general, the magnitude ofimpedance 210 must be larger than the resistance of R₂, typically (butnot limited to) at least ten times larger. To the extent that Z_(S) canbe represented by a resistance R_(S), a metric for the charging ofC_(LOAD) in FIG. 6 will be the charging time-constant parameterR_(S)(C_(LOAD)+C₂).

Referring now to FIG. 7 , an analog-hysteretic, two-position feedbacknetwork 303 (AHFN), functioning as the regulator 105 shown in FIG. 2 ,is added to circuit 200 of FIG. 4 to produce modified circuit 300. TheAHFN 303 regulates the peak output voltage so that it cannot rise abovea predetermined level even if discharge signal 203 has not yet turned ontransistor M₂ to initiate the discharge of C₂ and C_(LOAD). Feedbackresistors R₃ and R₄ in FIG. 7 form a voltage divider 301 that produces areduced version of V_(OUT) by attenuating it to a level consistent withthe limits of standard operational amplifiers or similar components,typically no larger than about 20 V. Because V_(OUT) can be in thekilovolt range, this feature is necessary for proper operation of AHFN303, as explained below. Note that R3 and R4 should be much larger thanR₂, a factor of at least ten times higher, to avoid R₃ and R₄ effectingthe discharge time of C_(LOAD).

AHFN 303 establishes a connection between the input voltage source 101and input 102 to the CBC, but only if output voltage 103 has not yetreached a predetermined value during the charging phase of C_(LOAD).Once the predetermined output voltage has been reached, AHFN 303temporarily disconnects the CBC from input voltage source 101.Reconnection occurs once C_(LOAD) has been discharged by resistor R₂ viatransistor M₂. This discharging occurs during the “on” phase of M₂.

Referring now to FIG. 8 , details of one embodiment of AHFN 303 areshown. A signal 204 (CHRG) is applied to the gate of p-channel MOSFETM₃, and signal 203 (DCHRG) is applied to both M₂ and the V⁻ input ofcircuit U₂. Operation of the circuit over one period of V_(OUT) isdescribed as follows: Charging signal CHRG and discharge signal DCHRGboth start in their low (“logic 0”) states. The low value of CHRG turnson p-channel MOSFET M₃, thereby connecting input voltage V_(DC) (101) tocascaded-boost converter 200. Resistor R₂ is also disconnected from thecircuit via MOSFET M₂, because DCHRG is also low, thereby placing M₂ inits off state. In one embodiment, the DCRHG signal may comprise a 5-Hz,50-percent duty cycle waveform that proceeds regardless of the output ofthe feedback network comprising R₃ and R₄. In one embodiment, U₁ is aSchmitt trigger whose output goes to its high (“logic 1”) when thefeedback voltage between R₃ and R₄ rises to 10 V; U₁ goes low again whenthe feedback voltage falls to 4 V. These values comprise the hysteresisvoltages of Schmitt trigger U₁ in the disclosed embodiment. Other valuesof these transition voltages can be used without departing from theintent of the invention.

For the purposes of this disclosure, a “Schmitt trigger” is a comparatorcircuit with hysteresis implemented by applying positive feedback to thenon-inverting input of a comparator or differential amplifier. Accordingto embodiments, a Schmitt trigger may be an active circuit whichconverts an analog input signal to a digital output signal. The Schmitttrigger may be a configured to include an output that retains its valueuntil the input changes sufficiently to trigger a change. In anon-inverting configuration, when the input is higher than a chosenthreshold, the output is high. According to embodiments, and further,configurations thereof, when the input is below a different (lower)chosen threshold the output is low, and when the input is between thetwo levels the output retains its value. This dual threshold action iscalled hysteresis and implies that the Schmitt trigger may possess amemory and can act as a bistable multivibrator (latch or flip-flop), inembodiments.

In embodiments, when the input to Schmitt trigger U₁ is 12 V, the outputof U₁ is forced to its high output state (e.g., “logic 1”), causingthree events occur: (1) The DCHRG signal is inverted by comparator U₂;(2) the summation circuit formed by two same-valued resistors R_(ADD),with their midpoint connected to the (−) input of operational amplifierU₃, then creates a voltage of 6 V at the V⁻ inverting input of U₃; and(3) the output of U₃ switches to its high voltage output state, thusturning off p-channel MOSFET M₃ connected between CBC 200 and DC source101. For the purposes of this disclosure, “comparator” is a device thatcompares two or more voltages or currents, and outputs a signalindicating which is larger. A comparator may include one or morespecialized high-gain differential amplifiers. The output of U₃ is heldhigh until DCHRG goes high, at which point M₂ turns on and discharges C₂and any C_(LOAD) connected in parallel with C₂. Here again, C_(LOAD) mayrepresent an EDS capacitance. During this time interval, M₂ will stillbe off, because the voltage at the noninverting input of U₃ will stillbe large enough to force the output of U₃ to its high voltage. Only whenDCHRG again goes low does M₃ turn back on. This operation ensures thatthe CBC will only charge C₂ and C_(LOAD) until the desired peak outputvoltage is reached. The resulting output 103 will thus take the form ofa 50% duty cycle output, even though the CBC has only operated for afraction of the portion of the cycle over which the output V_(OUT) ishigh. FIG. 9 shows a typical output waveform derived from the circuit ofFIG. 4 with the AHFN of FIG. 8 connected as in FIG. 7 . The outputwaveform may correspond to the interdigitated electrodes disposed on orin the EDS. The electrodes may be configured to produce one or moretraveling electrostatic fields, those in turn exerts a coulomb and otherforces on deposited particles, thereby transporting the particles to oneor more edges of the EDS. The traveling electrostatic field functions toclear the EDS of debris and increasing the effectiveness of the EDS,according to embodiments of the present subject matter. In solarapplications, this clearing of particles substantially restores thepower output of the collector, in embodiments wherein the EDS is aphotovoltaic panel. The electrostatic field may charge the dustparticles and remove the dust particles (or move to an acceptable degreeand area) without the need for physical contact. In embodiments theprocess of removing dust from an EDS (i.e., soiling) may be controlledmanually or automatedly by one or more computers, processors, systems,or combination thereof.

While the disclosed subject matter is described herein in terms ofcertain preferred embodiments, those skilled in the art will recognizethat various modifications and improvements may be made to the disclosedsubject matter without departing from the scope thereof. Moreover,although individual features of one embodiment of the disclosed subjectmatter may be discussed herein or shown in the drawings of the oneembodiment and not in other embodiments, it should be apparent thatindividual features of one embodiment may be combined with one or morefeatures of another embodiment or features from a plurality ofembodiments.

In addition to the specific embodiments claimed below, the disclosedsubject matter is also directed to other embodiments having any otherpossible combination of the dependent features claimed below and thosedisclosed above. As such, the particular features presented in thedependent claims and disclosed above can be combined with each other inother manners within the scope of the disclosed subject matter such thatthe disclosed subject matter should be recognized as also specificallydirected to other embodiments having any other possible combinations.Thus, the foregoing description of specific embodiments of the disclosedsubject matter has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit thedisclosed subject matter to those embodiments disclosed.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the method and system of thedisclosed subject matter without departing from the spirit or scope ofthe disclosed subject matter. Thus, it is intended that the disclosedsubject matter include modifications and variations that are within thescope of the appended claims and their equivalents.

What is claimed is:
 1. An AC power supply for connection to at least oneelectrode of an electrodynamic screen, the power supply comprising: aDC-to-DC converter electrically coupled to a source of DC voltage, theDC-to-DC converter further comprising an output of the DC-to-DCconverter; a DC-to-AC converter electrically coupled to the output ofthe DC-to-DC converter, the DC-to-AC converter comprising a two-terminalpassive element electrically coupled in series with a first transistor,the first transistor comprising a control terminal, wherein the controlterminal of the first transistor is electrically coupled to a periodicvoltage signal configured to switch the first transistor into an onstate and an off state; an AC output, the AC output comprising an ACvoltage configured to change periodically; a regulator circuitconfigured to sample the AC output voltage of the power supply, theregulator circuit further configured to detect when the AC outputvoltage reaches a predetermined voltage, and wherein; the regulatorcircuit is configured to electrically couple the power supply to thesource of DC voltage when the output voltage is less than thepredetermined voltage.
 2. The power supply of claim 1, wherein theperiodic voltage signal is configured to control the on/off state of theat least a transistor causes the AC output to transition periodically,at a predetermined frequency, between zero and a positive or negativevoltage of a magnitude larger than zero.
 3. The power supply of claim 2,wherein the periodic voltage signal comprises a frequency, the frequencyconfigured to vary.
 4. The power supply of claim 2, wherein the secondtransistor is a p-channel MOSFET.
 5. The power supply of claim 1,wherein the regulator circuit comprises a second transistor configuredto connect and disconnect the power supply to the source of DC voltage.6. The power supply of claim 1, wherein the DC-to-DC converter is acascaded-boost converter.
 7. The power supply of claim 6, wherein thecascaded-boost converter operates in a discontinuous mode.
 8. The powersupply of claim 1, wherein the output voltage is applied to at least oneelectrode of an electrodynamic screen, the electrode comprising acapacitance electrically coupled in parallel with the AC output of thepower supply.
 9. The power supply of claim 1, wherein the periodicvoltage signal configured to control the on/off state of the firsttransistor causes the AC output of the power supply to transitionperiodically between a positive voltage and a negative voltage.
 10. Thepower supply of claim 9, wherein the periodic voltage signal comprises afrequency, the frequency configured to change over time.
 11. The powersupply of claim 1, wherein the periodic voltage is produced by anastable multivibrator.
 12. The power supply of claim 1, wherein the ACoutput comprises a plurality of distinct AC outputs.
 13. The powersupply of claim 12, wherein the plurality of distinct AC outputs applypoly-phased voltages to a plurality of electrodes of an electrodynamicscreen.
 14. The power-supply circuits of claim 13, wherein the number ofpoly-phased voltages is between two and five.
 15. The power supply ofclaim 1, wherein the AC output voltage of the power supply is configuredto transition periodically between a voltage near zero and a voltage,wherein the voltage comprises a magnitude no larger than one kilovolt.16. The power supply of claim 15, wherein the magnitude of the AC outputvoltage of the power supply is configured to increase in magnitude to apredetermined value that is larger than one kilovolt.